Precipitation assimilation was used as a tool to understand the local dynamical mechanisms behind the 1993 Upper Mississippi River Basin floods. The assimilation of precipitation rates from the North American Regional Reanalysis by a regional climate model improved the upper-level dynamical features during the 1993 summer over the midwestern United States. The intensity and location of the subtropical upper-level westerly jet and its associated transverse circulations were noticeably improved in the regional simulations where the heavy precipitation core was found. This study suggests that the increased rainfall over the upper Mississippi River Basin during the 1993 summer was directly related with the location and intensity of the upper-level jet, and its associated transverse circulation, which might also increase low-level summertime meridional moisture transport from the Gulf of Mexico.